The long-term objectives of the proposed research is to construct transgenic mouse models that can be used for genetic toxicology and for predictive carcinogenesis. Current in vivo assays take 2 to 4 years, are expensive, use a large number of animals, high doses of the carcinogens and little information on the mechanism of the biologic activity of the chemicals is gained. Deletions are associated with carcinogenesis and inheritable disease. Assays to quantify the number of deletion events have been developed in preliminary studies in yeast, human cells and in vivo in the mouse. It has been shown that deletion events in all three systems are inducible with carcinogens that are positive in the Salmonella assay as well as with carcinogens that are negative in the Salmonella assay. The development of novel transgenic mouse assays allowing quantification of deletion events is proposed. The deletion substrates in the transgenic mice are designed so that the same deletion event can be selectable in tissue culture. The quantification of the deletion events in mice will be performed using quantitative PCR and/or immunohistochemical staining. These assays may require only a few mice per dose, may take only several weeks to perform and thus may require only modest funding in comparison to current assays. The assays may show a high predictability of a potential carcinogenic effect of chemicals. It may be possible to quantify deletions at low doses. Tissue and cell lineage specific effects should be detectable. Germ-line deletion events will be detected directly in germ cells or as deletion events inherited in all cells of one offspring. In addition, the same constructs scoring for the same genetic endpoint on a selective basis will be available in cell culture to allow in vivo - in vitro comparisons. Use of these transgenic mouse assay in toxicology may require less animals than current technology and may in turn enhance the use of the assays with the same genetic endpoint in tissue culture which may lead to a further reduction in the number of animals needed.